Today, smartphones and tablet PCs are used widely and high-capacity multimedia communications are activated, so mobile traffic is increasing rapidly. Mobile traffic is expected to continue to increase in the future, doubling in volume each year. Since most mobile traffic is transmitted through a base station, communication service providers are currently confronted with serious network overloads. In order to handle the increase in traffic, communication service providers are increasing the network equipment investment and commercializing the next generation of mobile communication standards (e.g., WiMAX, LTE (long term evolution), etc.) for efficiently handling a high volume of traffic in a hurry. Yet, in order to bear the expected increase in traffic even more rapidly, it is time to seek other solutions.
D2D (device-to-device) communication is a communication technology for directly delivering traffic between adjacent nodes. In a D2D communication environment, each node such as a mobile terminal and the like searches for another user equipment that is physically adjacent to the corresponding node, establishes a communication session, and then transmits traffic. Thus, since D2D communication can help solve the problem of traffic overload by distributing the traffic focused on a base station, D2D communication is spotlighted as an elementary technology of post-4G, next-generation mobile communication. Such standard organizations as 3GPP, IEEE and the like are promoting the enactment of a D2D communication standard based on LTE-A or Wi-Fi. Companies are developing an independent D2D communication technology.